Known in the art are such electronic percussion musical instruments which have music playing manipulation devices in the form of pads (i.e. playing pads) to be struck by the player and generate electronic musical tones resembling drum sounds and cymbal sounds when the pads are struck, such as disclosed in examined Japanese patent publication No. H5-64463 and issued U.S. Pat. No. 4,932,303. When the player strikes the playing pad, the impact strength of the strike onto the pad is detected by an impact sensor such as a piezoelectric element or device. The impact sensor generates a vibrating voltage having a maximum amplitude which depends on the strength of the strike, which is a manipulation quantity of the player.
FIG. 4 shows a circuit configuration of a drum pad circuit in a conventional device. The reference numeral 101 denotes a drum pad circuit, which is installed in the body of a drum pad. The drum pad circuit comprises a piezoelectric element 2, a resister 3 having a resistance value R1, a resister 102 having a resistance value RL, and a pad output terminal 12. The vibrating voltage generated by the piezoelectric element 2 is divided by the resisters 3 and 102, and outputted from the pad output terminal 12 as a pad output voltage.
FIG. 5a shows a block diagrammatic configuration of a conventional percussion voicing device consisting of a drum pad circuit and a voicing unit, and FIG. 5b is a graph showing a response characteristic of the voicing unit of FIG. 5a. In FIG. 5a, the drum pad circuit 101, the one shown in FIG. 4, detects a strike onto the pad and outputs the detection voltage at the pad output terminal 12, which in turn is connected to an input terminal 104 of a voicing unit 103, which generates a percussion tone signal or a percussion tone representing signal accordingly responsive to the detection voltage from the drum pad circuit 101. The voicing unit 103 is installed in a general-purpose electronic musical instrument or in a dedicated electronic percussion instrument. Or alternatively, the voicing unit 103 can be installed in the body of a drum pad device, or the drum pad device itself may be comprised in a general-purpose electronic musical instrument or a dedicated electronic percussion instrument.
In the voicing unit 103, the drum pad output voltage input to the input terminal 104 is input to an envelope shaping circuit 105, which produces envelope signal representing an envelope shape of the vibrating voltage from the drum pad circuit 101. The envelope shaping circuit 105 includes a half-wave or full-wave rectifier circuit and an integrator circuit connected in cascade to output an envelope wave formed by bridging the peaks (crests) of the respective cycles of the rectified waveform one after another. The output from the envelope shaping circuit 105 is input to an A/D (analog-to-digital) converter 106, which samples the envelope wave by a predetermined sampling rate to produce a train of digital values representing the shape of the envelope wave digitally.
A central processing unit (CPU) 107 executes a computer program using a read only memory (ROM) or a random access memory (RAM), not shown though, and detects the maximum amplitude value of the envelope wave. Typically, the peak value (crest value) of the first cycle of the vibrating voltage which is generated by a single strike will make the maximum amplitude value among the decaying vibrating wave cycles caused by the single strike. It is simply because of easiness of the signal processing that the vibrating voltage wave is shaped into an envelope waveform, but the input vibrating voltage wave itself or a half-wave rectified or full-wave rectified wave of the input vibrating voltage wave may be input to the A/D converter 106. The CPU 107 digitally outputs in real time the maximum amplitude value as an output representing the magnitude of the strike force at the time point when the maximum amplitude is detected as a moment (time point) of the strike. For example, the CPU 107 outputs a note-on event message under the MIDI protocol containing the maximum amplitude value as a velocity value in the MIDI message. The CPU further drives a tone signal generator 108 to generate, at the moment of the strike, a percussion tone wave signal having an amplitude which corresponds to the maximum amplitude value of the vibration. The generated percussion tone wave signal which is a digital signal is then converted to an analog tone wave signal by a sound system 109 to be emitted from a loudspeaker as audible sound.
The drum pad circuit 101 shown in FIG. 4, however, has a drawback in that the operating range (i.e. the dynamic range) of a percussion voicing device will be limited to some narrow extent, making it difficult to generate faithful sounds for both a very strong strike and a very weak (soft) strike, when combined with the voicing unit 103 shown in FIG. 5a. The graph of FIG. 5b explains the response characteristic of the voicing unit 103 representing the relationship between the input voltage (absolute value of instantaneous voltage) to the input terminal 104 taken in abscissa and the output (absolute value of instantaneous voltage) from the A/D converter 106, which output is the digital conversion from the analog envelope wave, taken in ordinate. The characteristic line consists of three segments 110a, 110b and 110c. Strictly speaking, the line segment 110b is stepwise, but for simplicity it is depicted in a straight line.
The output of the A/D converter 106 in the voicing unit 103 is a digital value which is proportional to the input voltage at the input terminal 104 as depicted generally by a line segment 110b. More specifically, however, the A/D converter 106 will not increase its output value beyond its operating range where the input value exceeds its upper limit value (max), and keeps its maximum digital value as shown by a line segment 110c. Thus the increase in the input voltage will not be reflected as an increase in the output digital value. On the other hand, the A/D converter 106 outputs a zero value where the input value does not exceed its lower limit value (min), which is equal to one half of the resolution, and its digital “0” value is maintained within a certain dead zone 111 as shown by a line segment 110a. In the case of an A/D converter 106 with a limited number of coding bits, the amount of this lower limit input value (min) is not negligible. Therefore, in order for the voicing unit 103 to output digital values which increase faithfully in accordance with the input voltage, the input voltage (absolute value of instantaneous value) should be within the response range between the lower limit input value (min) and the upper limit input value (max). Where the operating range of the A/D converter 106 is narrow, the upper limit input value (max) cannot be high enough, and where the resolution is low (i.e. the number of coding bits is small), the lower limit input value (min) cannot be small enough, the response range will be narrow accordingly.
The problem in connection with the A/D converter 106 has been described above. In addition, there can be a problem that the voicing unit 103 may operate erroneously when the magnitude of the input voltage is small as compared with the noise level in the unit. Further, depending on a specific circuit configuration of the envelope shaping circuit 105, a small input voltage may not give an output due to the diodes included in the rectifying circuit, which means the envelope shaping circuit 105 also has a restriction of a lower limit input value (min). Still further, where the vibrating voltage is amplified through an amplifier, the amplifier may place a restriction of an upper limit input value (max) due to the saturation phenomenon of the amplifier.
Thus, in order for the voicing unit 103 to respond to any maximum amplitude values of the vibrating voltage, there is a restriction as to the input range of the maximum amplitude values of the vibrating voltage. To cope with such a restriction, it will be necessary to properly adjust or set the division ratio by the resistors 3 and 102 in the drum pad circuit 101 shown in FIG. 4, so that the maximum amplitude values of the vibrating voltage outputted from the drum pad circuit 101 should not exceed the above-described input range of the voicing unit 103 within the range of strength of the strikes given by the player.
On the other hand, the division ratio by the resistors should be set rather high so that the maximum amplitude value of the vibrating voltage outputted from the drum pad circuit 101 should not fall within the dead zone 111 as shown in FIG. 5b, even when the player strikes the drum pad weakly. Then, trouble is that the maximum amplitude values of the vibrating voltage would exceed the upper limit input value (max) while the strength of the strikes is not so large yet. As a result, even though the player strikes the pad strongly, the maximum amplitude values of the vibrating voltage outputted from the A/D converter 106 would not be accordingly high.